1. Field of the Invention
The disclosure herein relates to a vehicle electronic control system in which plural electronic control units are connected. Particularly, the disclosure relates to a vehicle electronic control system in which closely related processes are executed by separate electronic control units, a vehicle electronic control unit, and a vehicle control synchronization method.
2. Description of the Related Art
Electronic control units (“ECU”) mounted on a vehicle are required to control increasingly sophisticated and complicated functions, and it is becoming increasingly difficult to implement all of the required functions on a single ECU. Processes which are preferably executed by a single ECU may be executed by separate ECUs. However, when a process that is preferably executed by a single ECU is divided into two processes, for example, the processes need to be synchronized because the divided processes are closely related to each other.
FIGS. 1A, 1B, and 1C illustrate an example of synchronization of two processes. FIG. 1A illustrates a chronological relationship of two processes A and B executed by a single ECU. Because the process A and the process B are closely related to each other, the ECU executes the process A and then starts to execute the process B (following a minimum required time for switching of the processes). For example, the ECU controls an actuator A based on a result of the process A and then controls a related actuator B based on a result of the process B. In this way, the two actuators can be controlled in a coordinated manner. Predetermined times (which may be referred to as “control periods”) are allocated to the processes A and B. For example, a sufficient time for the process A is allocated to a control period A, and a sufficient time for the process B is allocated to a control period B.
FIGS. 1B and 1C illustrate examples of a chronological relationship between the processes A and B where the process A is processed by an ECU_A and the process B is processed by an ECU_B. The ECU_A and the ECU_B are electrically connected to each other. Unless the processes are synchronized between the ECU_A and the ECU_B, a desired chronological relationship between the processes A and B may be broken. For example, a blank time may arise between the end of the process A and the start of the process B (FIG. 1B), or the process B may be started when the process A is not yet completed (FIG. 1C). In the case of FIG. 1B, the control of an actuator B following the control of an actuator A is delayed. In the case of FIG. 1C, the actuator B cannot be properly controlled because the control of the process B is based on the result of the process A. Thus, in either case, the actuators A and B cannot be controlled in a smoothly coordinated manner.
According to a process synchronization technology discussed in Patent Document 1, in a clustered computer including plural computers, one computer notifies another computer of the start and end of a session in an asynchronous manner. Specifically, a master computer notifies a slave computer of the start and end timings of a parallel process portion.
In another technology discussed in Patent Document 2, processes are executed simultaneously by a master node and a slave node. Specifically, Patent Document 2 discusses a parallel computer in which a master node transmits a synchronization signal to a slave node, stands by for a pre-measured transmission time, and then executes a process simultaneously with the slave node.
However, when a process that is preferably executed by a single ECU is executed by separate ECUs, the response characteristics of the entire system are affected according to the synchronizing technology of Patent Document 1, resulting in the need for re-adaptation.
In the synchronizing technology according to Patent Document 2, although the transmission time is measured (estimated) in advance, it is difficult to completely match the execution times of the master node and the slave node. For example, if the slave node starts a process before the master node, the slave node may not be able to execute the process by utilizing the result of the process executed by the master node. Namely, the synchronizing technology according to Patent Document 2 does not take into consideration the case where a process that is preferably executed by a single ECU is executed by separate ECUs.
Thus, it has been difficult for the process synchronization methods according to the related art to synchronize two closely related processes so that the processes can be controlled in a synchronized manner. In this respect, in the case of a simple information process not related to control, not much of a problem may be caused even when the ECU_B fails to execute its process once. However, there has been no technology capable of addressing the need for controlling closely related processes by separate ECUs, such need being unique to control systems.    Patent Document 1: Japanese Laid-open Patent Publication No. 2006-228192    Patent Document 2: Japanese Laid-open Patent Publication No. 2005-071280